GHC 7.0.4 recursion while trying to derive type

[Christian Maeder]

Am 08.01.2012 04:39, schrieb Bogdan Opanchuk:
> Hello,
>
> Consider the following code:
>
>
> {-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, OverlappingInstances,
>         UndecidableInstances, FunctionalDependencies #-}

We have also such (cruel) code using these extension.

>
> t4.hs:17:31:
>     Context reduction stack overflow; size = 21
>     Use -fcontext-stack=N to increase stack size to N

Our code compiles with ghc-7-0.4 if we add -fcontext-stack=31 to the ghc 
command line.

Does your code compile with an increased (try 100) context-stack?

[..]

> So, the question is, could anyone please tell me, is what I am trying
> to do actually correct, and what was changed from 7.0.4 to 7.2.2 to
> make it work?

I cannot answer this, but our code also compiles with ghc-7.2.2 using a 
lower context-stack (of 26).

HTH Christian

>
> Thank you in advance.
>
> Best regards,
> Bogdan